Winemakers have recognized for a long time that wines young in age have a sour flavor which renders them unpalatable. The sourness in young wines comes from high levels of tannin. Typically, one must wait from several months to years for tannins to oxidize naturally before a wine emerges with a desirable organoleptic character.
Present in the juice and skins of wine grapes, tannins are solvated into the wine must, and becomes part of the young wine. Chemically, the natural tannin found in wine grapes is formed by the polymerization of elementary phenolic molecules. These water soluble compounds have a molecular weight between 500 and 3000 and are known as condensed tannins. Typically, they are condensed polymers from 3-flavanols (catechins) and 3-4 flavandiols (leucoanthocyanidin).
However, another group of tannin compounds can also be found in wines. By law, one may add tannins to wine, e.g., tannic acid. Also, when one stores wine in oak casks, tannins leach out of the wood and into the wine. These tannins are referred to as hydrolyzable tannins, differing from the condensed tannins in that they are composed of one glucosidic molecule bonded to a phenolic moiety, e.g., gallic acid or ellagic acid.
Whatever the source, the problem remains the same--high tannin equals sourness. It would be most beneficial and expedient to remove or reduce the tannin content of young wines, instantly producing a palatable wine months ahead of schedule.